Wearable devices that wirelessly connected to a speech translation computer.

Niven provides a realistic version of a universal translator in Ringworld.

"Stay on your vehicles," Speaker ordered in a low voice. "Wait until they reach us. Then dismount. I assume we are all wearing our communicator discs?"

Louis wore his inside his left wrist. The discs were linked to the autopilot aboard the Liar. They should work over such a distance, and the Liar's autopilot should be able to translate any new language...

The tattooed one made a short speech. That was luck. The autopilot would need data before it could begin a translation...

Presently the discs were filling in words and phrases... His voice was almost a chant, almost a recital of poetry. The autopilot was translating Louis's words into a similar chant, though it spoke to Louis in a conversational tone. Louis could hear the other translator discs whistling softly in Puppeteer, snarling quietly in the Hero's Tongue.

Rather than just presenting a magical device, Niven makes sure you know that interpreting speech is a processor intensive task, and might be best done centrally. Also, he notes that the machine needs a good-sized sample before translation is possible.